Epithelial tumor development is the result of altered tissue homeostasis, due to deranged intracellular regulation and escape from the counteracting influences of a normal cellular environment. We plan to continue our work in this area, as it relates to the function of the three TGF-beta isoforms in the skin. Mice with specific knockout mutations of the TGF-beta1, TGF-beta2 and TGF-beta 3 genes have been recently developed. Homozygous TGF-beta 2 and TGF-beta 3 knockout mice die within a few hours after birth. To overcome this problem, we have developed a full-thickness grafting approach. When the skin of the newborn knockouts is grafted onto nude mice, it develops normally and can be maintained on the host for at least 1 year. We will use this approach to address the following questions: 1) TGF-beta control of keratinocyte growth and differentiation in vivo. We will test the hypothesis that the individual TGF-beta isoforms play distinct or only partially overlapping roles on control of keratinocyte growth/differentiation and apoptosis in the intact skin. We will analyze the epidermis of grafts from mice with each of the TGF- beta knockout mutations, as well as wild type controls, under basal conditions and under conditions of altered skin homeostasis, such as after TPA or retinoic acid exposure. 2) TGF-beta control of keratinocyte growth and differentiation in culture. We will complement the in vivo analysis with in vitro studies of cultured kerationocytes derived from both knockout and wild type mice, plus/minus TGF-beta exposure. In this manner, we will determine (1) which are the direct and specific effects of individual TGF-betas on keratinocyte growth, differentiation and apoptosis; (2) which of these effects are due to an autocrine versus paracrine loop. 3) TGF-beta control of skin tumor development. We will investigate the role that the individual TGF-betas play in skin carcinogenesis, with a special emphasis on TGF-beta3. For this purpose, TGF-beta knockout skins grafted onto nude mice will be tested for their rate of benign and malignant tumor formation, in response to a chemical carcinogenesis protocol or after crossing into a ras transgenic background. 4) TGF-beta control of keratinocyte tumorigenicity. The individual TGF-beta factors could play distinct autocrine and/or paracrine functions in control of keratinocyte tumor development. To address this question, we will evaluate (a) keratinocytes derived from TGF-beta knockout mice for their susceptibility to tumorigenic conversion after ras oncogene transformation, and (b) dermal fibroblasts derived from the same mice for their capability to suppress keratinocyte tumor formaiton.